src/llvm/lib/Support/LockFileManager.cpp

   1 //===--- LockFileManager.cpp - File-level Locking Utility------------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 #include "llvm/Support/LockFileManager.h"
  10 #include "llvm/ADT/STLExtras.h"
  11 #include "llvm/ADT/StringExtras.h"
  12 #include "llvm/Support/Errc.h"
  13 #include "llvm/Support/FileSystem.h"
  14 #include "llvm/Support/MemoryBuffer.h"
  15 #include "llvm/Support/Path.h"
  16 #include "llvm/Support/raw_ostream.h"
  17 #include <sys/stat.h>
  18 #include <sys/types.h>
  19 #if LLVM_ON_WIN32
  20 #include <windows.h>
  21 #endif
  22 #if LLVM_ON_UNIX
  23 #include <unistd.h>
  24 #endif
  25 using namespace llvm;
  26
  27 /// \brief Attempt to read the lock file with the given name, if it exists.
  28 ///
  29 /// \param LockFileName The name of the lock file to read.
  30 ///
  31 /// \returns The process ID of the process that owns this lock file
  32 Optional<std::pair<std::string, int> >
  33 LockFileManager::readLockFile(StringRef LockFileName) {
  34   // Read the owning host and PID out of the lock file. If it appears that the
  35   // owning process is dead, the lock file is invalid.
  36   ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
  37       MemoryBuffer::getFile(LockFileName);
  38   if (!MBOrErr) {
  39     sys::fs::remove(LockFileName);
  40     return None;
  41   }
  42   MemoryBuffer &MB = *MBOrErr.get();
  43
  44   StringRef Hostname;
  45   StringRef PIDStr;
  46   std::tie(Hostname, PIDStr) = getToken(MB.getBuffer(), " ");
  47   PIDStr = PIDStr.substr(PIDStr.find_first_not_of(" "));
  48   int PID;
  49   if (!PIDStr.getAsInteger(10, PID)) {
  50     auto Owner = std::make_pair(std::string(Hostname), PID);
  51     if (processStillExecuting(Owner.first, Owner.second))
  52       return Owner;
  53   }
  54
  55   // Delete the lock file. It's invalid anyway.
  56   sys::fs::remove(LockFileName);
  57   return None;
  58 }
  59
  60 bool LockFileManager::processStillExecuting(StringRef Hostname, int PID) {
  61 #if LLVM_ON_UNIX && !defined(__ANDROID__)
  62   char MyHostname[256];
  63   MyHostname[255] = 0;
  64   MyHostname[0] = 0;
  65   gethostname(MyHostname, 255);
  66   // Check whether the process is dead. If so, we're done.
  67   if (MyHostname == Hostname && getsid(PID) == -1 && errno == ESRCH)
  68     return false;
  69 #endif
  70
  71   return true;
  72 }
  73
  74 LockFileManager::LockFileManager(StringRef FileName)
  75 {
  76   this->FileName = FileName;
  77   if (std::error_code EC = sys::fs::make_absolute(this->FileName)) {
  78     Error = EC;
  79     return;
  80   }
  81   LockFileName = this->FileName;
  82   LockFileName += ".lock";
  83
  84   // If the lock file already exists, don't bother to try to create our own
  85   // lock file; it won't work anyway. Just figure out who owns this lock file.
  86   if ((Owner = readLockFile(LockFileName)))
  87     return;
  88
  89   // Create a lock file that is unique to this instance.
  90   UniqueLockFileName = LockFileName;
  91   UniqueLockFileName += "-%%%%%%%%";
  92   int UniqueLockFileID;
  93   if (std::error_code EC = sys::fs::createUniqueFile(
  94           UniqueLockFileName.str(), UniqueLockFileID, UniqueLockFileName)) {
  95     Error = EC;
  96     return;
  97   }
  98
  99   // Write our process ID to our unique lock file.
 100   {
 101     raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true);
 102
 103 #if LLVM_ON_UNIX
 104     // FIXME: move getpid() call into LLVM
 105     char hostname[256];
 106     hostname[255] = 0;
 107     hostname[0] = 0;
 108     gethostname(hostname, 255);
 109     Out << hostname << ' ' << getpid();
 110 #else
 111     Out << "localhost 1";
 112 #endif
 113     Out.close();
 114
 115     if (Out.has_error()) {
 116       // We failed to write out PID, so make up an excuse, remove the
 117       // unique lock file, and fail.
 118       Error = make_error_code(errc::no_space_on_device);
 119       sys::fs::remove(UniqueLockFileName.c_str());
 120       return;
 121     }
 122   }
 123
 124   while (1) {
 125     // Create a link from the lock file name. If this succeeds, we're done.
 126     std::error_code EC =
 127         sys::fs::create_link(UniqueLockFileName.str(), LockFileName.str());
 128     if (!EC)
 129       return;
 130
 131     if (EC != errc::file_exists) {
 132       Error = EC;
 133       return;
 134     }
 135
 136     // Someone else managed to create the lock file first. Read the process ID
 137     // from the lock file.
 138     if ((Owner = readLockFile(LockFileName))) {
 139       // Wipe out our unique lock file (it's useless now)
 140       sys::fs::remove(UniqueLockFileName.str());
 141       return;
 142     }
 143
 144     if (!sys::fs::exists(LockFileName.str())) {
 145       // The previous owner released the lock file before we could read it.
 146       // Try to get ownership again.
 147       continue;
 148     }
 149
 150     // There is a lock file that nobody owns; try to clean it up and get
 151     // ownership.
 152     if ((EC = sys::fs::remove(LockFileName.str()))) {
 153       Error = EC;
 154       return;
 155     }
 156   }
 157 }
 158
 159 LockFileManager::LockFileState LockFileManager::getState() const {
 160   if (Owner)
 161     return LFS_Shared;
 162
 163   if (Error)
 164     return LFS_Error;
 165
 166   return LFS_Owned;
 167 }
 168
 169 LockFileManager::~LockFileManager() {
 170   if (getState() != LFS_Owned)
 171     return;
 172
 173   // Since we own the lock, remove the lock file and our own unique lock file.
 174   sys::fs::remove(LockFileName.str());
 175   sys::fs::remove(UniqueLockFileName.str());
 176 }
 177
 178 LockFileManager::WaitForUnlockResult LockFileManager::waitForUnlock() {
 179   if (getState() != LFS_Shared)
 180     return Res_Success;
 181
 182 #if LLVM_ON_WIN32
 183   unsigned long Interval = 1;
 184 #else
 185   struct timespec Interval;
 186   Interval.tv_sec = 0;
 187   Interval.tv_nsec = 1000000;
 188 #endif
 189   // Don't wait more than five minutes for the file to appear.
 190   unsigned MaxSeconds = 300;
 191   bool LockFileGone = false;
 192   do {
 193     // Sleep for the designated interval, to allow the owning process time to
 194     // finish up and remove the lock file.
 195     // FIXME: Should we hook in to system APIs to get a notification when the
 196     // lock file is deleted?
 197 #if LLVM_ON_WIN32
 198     Sleep(Interval);
 199 #else
 200     nanosleep(&Interval, nullptr);
 201 #endif
 202     bool LockFileJustDisappeared = false;
 203
 204     // If the lock file is still expected to be there, check whether it still
 205     // is.
 206     if (!LockFileGone) {
 207       if (sys::fs::access(LockFileName.c_str(), sys::fs::AccessMode::Exist) ==
 208           errc::no_such_file_or_directory) {
 209         LockFileGone = true;
 210         LockFileJustDisappeared = true;
 211       }
 212     }
 213
 214     // If the lock file is no longer there, check if the original file is
 215     // available now.
 216     if (LockFileGone) {
 217       if (sys::fs::exists(FileName.str())) {
 218         return Res_Success;
 219       }
 220
 221       // The lock file is gone, so now we're waiting for the original file to
 222       // show up. If this just happened, reset our waiting intervals and keep
 223       // waiting.
 224       if (LockFileJustDisappeared) {
 225         MaxSeconds = 5;
 226
 227 #if LLVM_ON_WIN32
 228         Interval = 1;
 229 #else
 230         Interval.tv_sec = 0;
 231         Interval.tv_nsec = 1000000;
 232 #endif
 233         continue;
 234       }
 235     }
 236
 237     // If we're looking for the lock file to disappear, but the process
 238     // owning the lock died without cleaning up, just bail out.
 239     if (!LockFileGone &&
 240         !processStillExecuting((*Owner).first, (*Owner).second)) {
 241       return Res_OwnerDied;
 242     }
 243
 244     // Exponentially increase the time we wait for the lock to be removed.
 245 #if LLVM_ON_WIN32
 246     Interval *= 2;
 247 #else
 248     Interval.tv_sec *= 2;
 249     Interval.tv_nsec *= 2;
 250     if (Interval.tv_nsec >= 1000000000) {
 251       ++Interval.tv_sec;
 252       Interval.tv_nsec -= 1000000000;
 253     }
 254 #endif
 255   } while (
 256 #if LLVM_ON_WIN32
 257            Interval < MaxSeconds * 1000
 258 #else
 259            Interval.tv_sec < (time_t)MaxSeconds
 260 #endif
 261            );
 262
 263   // Give up.
 264   return Res_Timeout;
 265 }